1. Field of the Invention
This invention relates to an automatic document feeder operable with one driving means, and more particularly to a document feeder capable of automatically feeding original documents to be treated one by one to a document handling device such as a copying machine at high speed with a high efficiency by using only a single motor.
2. Description of the Prior Art
There have been so far proposed a variety of document feeders for automatically supplying and discharging original documents one by one to and from a document handling device such as an electrostatic copying machine, printer, image scanner and facsimile. Generally, the document feeder comprises a document supply unit for feeding out original documents one by one from a supply tray and transferring the original document to a document reading portion defined on the document handling device through a document supply passage, and a document discharge unit for sending out the document from the document reading portion to a discharge tray after treating the document. For instance, in the copying machine, the document feeder is pivotally laid on an upper surface with a platen of the machine, onto which the original document is supplied to optically read an image on the document.
The document feeders are grouped into two types, one having the document supply unit and document discharge unit which are opposed to each other astride the document reading portion, and other type having the document supply unit integrated with the document discharge unit on one side of the document reading portion. The automatic document feeders disclosed in U.S. Pat. Nos. 5,083,766; 5,280,330; 5,327,205 and 5,377,966 are typical of the former type. The document feeders of the latter type have been known by U.S. Pat. No. 4,922,292, Japanese Patent Application Public Disclosures Nos. SHO 61(1986)-295946(A) and HEI 1(1989)-127557(A), and Japanese Utility Model Public Disclosure No. SHO 58(1983)-34128(A).
The document feeder of the latter type having the united document supply and discharge units arranged on one side of the document reading portion can be made simple in structure and compact as schematically shown in FIG. 1 as one example.
As illustrated, this conventional document feeder comprises a document supply unit 1 for supplying an original document D1 to a document reading portion p2 defined on a platen P of a copying machine through a document supply passage p1, a document positioning unit 2 for transferring the document fed to the document reading portion p2 so as to place the tail end of the document D2 at a prescribed reading reference point X, and a document discharge unit 3 for sending out the document D3 from the document reading portion p2 via a document discharge passage p3 after copying.
The document supply unit 1 includes a document supply tray 1a for stacking the original documents thereon, a document separation means 1b for allowing only one document to pass therethrough, and paired register rollers 1c for performing skew correction of the document being forwarded through the document supply passage p1.
The document discharge unit 3 includes one or more discharge rollers 3a on the document discharge passage p3 so as to send out the document D2 from the document reading portion p2 to a document discharge tray 3b.
The document positioning unit 2 is formed of an endless belt with which the platen P is overlaid entirely or partially as proposed in U.S. Pat. No. 4,922,292. The document positioning unit 2 serves to not only place the document D2 at the reading position, but also feed out the document into the discharge passage p3 as indicated by D3.
In FIG. 1, reference numeral 4 denotes a gate member for aligning the tail end of the document D2 fed into the document reading portion p2 with the reading reference point X, and numeral 5 denotes a flap for switching over the document supply passage p1 and discharge passage p3 relative to the reading portion p2.
When feeding the original document D1 from the supply tray 1a to the document reading portion p2 through the document supply passage p1, the document separation means 1b is first driven to take out one original document D1 from the supply tray 1a and forward the document D1 to the register rollers 1c. To perform skew correction, the register rollers 1c are at a stop until the leading end of the document D1 comes into slight collision therewith and start to rotate to forward the document D1 to the reading portion p2 on the platen P immediately after the collision of the document with the register rollers. At this time, the gate member 4 assumes its lower position, and the switching flap 5 assumes its upper position so as to permit the document D1 to pass.
The document fed through the supply passage p1 is sent into the document reading portion p2 until the tail end of the document goes across the reading reference point X as indicated by D2 by driving the document positioning unit 2 in the forward direction d1. When the document D2 passes through the reading reference point X, the gate member 4 rises, and then, the document D2 is moved backward by driving the document positioning unit 2 in the reverse direction d2 until the tail end thereof collides with the gate member 4 so as to place the document D2 at the prescribed reading position on the platen P when the document D2 collides with the gate member 4, the document positioning unit 2 is stopped for carrying out the copying operation. Upon completion of copying, the gate member 4 and the switching flap 5 are lowered, and then, the document positioning unit 2 is driven in the reverse direction d2 to send out the document D2 from the document reading portion p2 to the document discharge passage p3.
Thus, in order to forward the document from the supply tray 1a to the document reading portion p2 through the supply passage p1 and further to the discharge tray 3b through the discharge passage p3, the separation means 1b, register rollers 1c, document positioning unit 2, and discharge rollers 3a must be operated by controlling exclusive driving motors independently with exquisite timing.
That is, at least three motors M1, M2 and M3 are required for driving the document supply unit 1, document positioning unit 2 and the document discharge unit 3, respectively as illustrated. In this mechanism, the separation means 1b and the register rollers 1c must be operated differentially, albeit by one motor M1, as touched upon above. Therefore, an electromagnetic clutch 6 is required for deactivating the register rollers 1c until the document forwarded by the separation means 1a collides with the register rollers.
Furthermore, the document feeder of this type calls for a plurality of driving means such as electric solenoid for operating the gate member 4 and the switching flap 5 in addition to the plurality of motors M1-M3 for driving the document supply unit 1, document positioning unit 2 and document discharge unit 3, and the electromagnetic clutch 6 provided to the register rollers 1c, resulting in a large overall size and complexity of the document feeder.
Moreover, recently, a need has been felt for a small and lightweight automatic document feeder capable of efficiently transferring the original document at high speed. Although the original document can be transferred fast even by speeding up the moving components in the document feeder, the document may possibly incur damage particularly when coming into collision with the register rollers and the gate member.